At one point, the group observed a striking yellow-and-black beetle laying eggs on a decaying birch stump. A parasitic wasp appeared to be following it, also laying eggs. Richard Saul took some photographs, which were passed on to experts for identification.

The beetle was quickly identified by Steven Falk of the Warwickshire Museum as Strangalia quadrifasciata, a longhorn beetle already recorded from the Park. The wasp proved more difficult, but was eventually identified as Helconidea ruspator by Gavin Broad, the hymenoptera specialist at the Natural History Museum, London.

Helconidea ruspator – notice the very long ovipositor(Original photograph by Richard Saul)

Helconidea ruspator is apparently very rarely recorded; the Natural History Museum have only one recent specimen. There were no previous records from Sutton Park of the family (Braconidae), let alone the species itself.

Mike Bloxham discovered some interesting information in Rev. T.A. Marshall's "Monograph of British Braconidae" (Transactions of the Entomological Society of London, pp.149-211, 1889). Marshall records the breeding of H. ruspator (then called Helcon ruspator) from a larva of Strangalia quadrifasciata. So it seems likely that the wasp was either attempting to place its eggs near the eggs of the beetle, so that its grubs could parasitize the emerging beetle larvae, or that the stump had already been used by other Strangalia quadrifasciata individuals and the wasp could detect the larvae.

Identification

Solitary wasps, such as Helconidea ruspator, are hymenopterans, i.e. members of the Order Hymenoptera, which includes bees, wasps, ants and similar species. About 6,500 hymenopterans occur in the British Isles. Of these, many sawflies (Sub-order Symphyta) and ichneumons (Superfamily Ichneumonoidea) are superficially similar to Helconidea ruspator. Identification of most hymenopterans is a highly skilled task, often requiring a microscope.

There are said to be about 3,000 species of ichneumon wasp in the British Isles, of which about 1,000 are brachonids (the family to which Helconidea ruspator belongs). It's almost certain that more brachonids would be found in Sutton Park if an expert carried out a survey.

Crucial points of identification for Helconidea ruspator are:

The clear presence of a narrow 'waist', more-or-less between the thorax and the abdomen (this is absent in sawflies). The waist doesn't show at all clearly in the photograph above; it's often best seen by looking at the insect from the side, since it can be obscured by the wings. (Although still slightly obscured by a wing, it's visible in this image of a different species of braconid wasp.)

The very long ovipositor of females. The ovipositor is absent altogether in males.

The hind legs, which are very noticeably different from the other two pairs of legs, being both larger (particularly the femur -- the largest section of the leg) and redder.

After this event was reported in the press (see below), a number of people sent me photographs or showed me specimens which they thought might be Helconidea ruspator, although none were. An ichneumon wasp called Pimpla rufipes (synonym P. hypochondriaca) seems to be common around houses in Sutton Coldfield in the autumn, and was regularly mistaken for Helconidea ruspator. However, in this species:

the ovipositor of the female is thicker and much shorter

all three pairs of legs are a similar colour

the hind pair of legs is only slightly larger than the other pairs

the 'waist' between the thorax and abdomen is much shorter.

Pimpla rufipes(Original photograph by Peter Coxhead)

Reports of this event

Versions of this story appeared in the Sutton Coldfield Observer (2 Oct 2009), the Birmingham Post (12 Oct 2009) and the Sutton Coldfield News (16 Oct 2009).